1. Field of the Invention
The present invention relates to a lock mechanism, which is used with a fluid pressure-operated apparatus that is driven by a pressure fluid. In particular, the present invention relates to a lock mechanism used with a fluid pressure-operated apparatus, which is capable of restricting displacement of a piston in a cylinder body.
2. Description of the Related Art
A pressure fluid-operated apparatus (for example, a cylinder apparatus), which is driven by a pressure fluid, has hitherto been used as a driving mechanism for transporting and positioning a workpiece, or as a driving mechanism for driving various types of industrial machinery.
For example, the cylinder apparatus, which as described above functions as a fluid pressure-operated apparatus, has a piston that is displaceable in an axial direction of a cylinder body having a cylindrical shape. When a pressure fluid is supplied from a supply port to a cylinder chamber, which is formed between the cylinder body and the piston, the piston is displaced along the cylinder body under a pressing action of the pressure fluid. The aforementioned cylinder apparatus occasionally is provided with a lock mechanism that restricts displacement of the piston so that a workpiece transported by the cylinder apparatus may be retained at a desired position.
The lock mechanism includes a retaining section, which protrudes at one end of the piston. A cylindrical buffer is installed in a hole disposed at an end of the cylinder body that is opposed to the retaining section. When the piston is displaced, the retaining section is inserted into the buffer, whereby a retaining operation is effected as a result of contact between the retaining section and the buffer. Accordingly, the retaining section is retained by the buffer, thereby providing a locked state in which displacement of the piston provided with the retaining section is restricted (see, for example, German Utility Model No. 29920639).
In the conventional technique described above, the buffer, which constitutes the lock mechanism, is formed of an elastic material that expands diametrally in order to retain the retaining section. Therefore, when the lock mechanism is used over several years, abrasions, permanent set in fatigue and/or settling may arise in the buffer due to contact action between the retaining section and the buffer. Further, the retaining force exerted on the retaining section by the buffer may be lowered. As a result, it may become difficult to reliably restrict displacement of the piston. Further, the retaining force exerted on the retaining section by the buffer in the lock mechanism, and the retaining state for restricting displacement of the piston, tend to become unstable.